1. Field of the Invention
This invention relates to a screen textile material.
2. Description of Related Art
To realize high density and high precision printing by means of a screen textile material, the screen textile material needs to be placed possibly with a high tension, to have a smaller size change rate, and to have a large elastic recovery rate. Although screen textile materials using a fiber made of flexible polymers such as nylon and polyester are widely used, such screen textile materials have a low strength and a modulus of elasticity and do not have a satisfactory size stability.
For high performance printing areas such as for printing on printed circuit boards, a screen textile material made of fine stainless wires has been used, but the stainless wires raise a problem to make handling of the material uneasy. To solve such a problem, a screen textile material made of a thermotropic liquid crystalline polyester fiber has been proposed as disclosed in Japanese Unexamined Patent Publications (KOKAI), Heisei No. 2-80,640 and Heisei No. 3-220,340, etc.
Though the screen textile material made of only the thermotropic liquid crystalline polyester has no problem in terms of strength and modulus of elasticity, the material is easily made fibrillated because made from rigid polymers, so that the fibrils generated during the weaving process raise problems that the fibrils disturb permeability of ink and impair high precision printing.
Some screen textile materials are proposed to be formed of an islands-in-sea type fiber in which a thermotropic liquid crystalline polyester makes island components and a polyethylene-terephthalate makes a sea component, or a core and sheath type conjugate fiber in which a thermotropic liquid crystalline polyester makes a core component and another flexible polymer makes a sheath component. With those materials, however, the flexible polymers constituting the sheath or sea components, because of not drawn, are very brittle and have problems not only that their mechanical strength is not adequate but also that the sheath portions are easily exfoliated or dropped. If a ratio of the island components or core components were made higher to obtain adequate mechanical feature, the core components might have been exposed, thereby reducing abrasive resistance, and rendering productions as a business operation extremely hard.
To solve the above problems, the inventors have proposed a screen textile material using a core and sheath type conjugate fiber in which a core component is formed of a thernotropic liquid crystalline polyester (A polymer) and a sheath component is formed by blending a flexible thermoplastic polymers (B polymer) and a thermotropic liquid crystalline polyester (C type), as disclosed in Japanese Unexamined Patent Publications (KOKAI), Heisei No. 5-230,715 and Heisei No. 8-260,249. Such a screen textile material has a good size stability, good mechanical property and good resistance against fibrils. The material has property more satisfactory than that made of fine stainless wires.